The present invention relates to a method of forming a titanium film and a barrier film on a surface of a substrate through lamination. In the present invention, a substrate (e.g., a silicon substrate) on a surface of which a titanium film and a barrier film need to be formed is the object of the processing. Typically, the present invention relates to a method of forming, through lamination, a titanium film and a barrier film on a surface of a semiconductor substrate formed of a silicon substrate in which contact holes and/or via holes are formed.
Forming a titanium film and a barrier film on a surface of a substrate through lamination is, for example, required for realizing the ohmic electrical connection with the surface of the substrate.
For example, in the field of recent semiconductor devices, the high density and the high integration have been required. In order to cope with this requirement, it is implemented that the multilayer metallization structure is formed on the silicon substrate. In this multilayer metallization structure, contact holes are formed in order to connect electrically therethrough a device of the lower layer and an aluminium wiring of the upper layer with each other. In addition, via holes are formed in order to connect electrically the aluminium wiring of the lower layer and the aluminium wiring of the upper layer with each other. Then, in order to realize the electrical connection therebetween through the holes, the holes are filled with filling metal such as aluminium, aluminium alloy or tungsten alloy. If the filling metal comes in direct contact with the silicon substrate or the aluminium wiring, then this will exert a bad influence (e.g., destruction of the diffused layers, and the like) on the silicon substrate or the multilayer metallization structure. The influence results from the phenomenon such as the suction effect (diffusion effect) between the silicon substrate or the multilayer metallization structure and the filling metal, and the like. This phenomenon is especially unpreferable in the current semiconductor device for which both the power saving and high speed operation are required. On the other hand, in the process in which tungsten alloy is employed as filling metal, WF6 is used as one of the process gases. WF6 penetrates into the silicon substrate to degrade its electrical characteristics and the like. This phenomenon is also unpreferable. In order to prevent these phenomena, before the contact holes, the via holes and the like are filled with a filling metal, the barrier layer is formed thinly so as to cover the sides of these holes and/or their peripheral areas. This barrier layer may be made of titanium nitride (TiN).
Now, the description will hereinbelow be given with respect to the structure in which the barrier layer is formed in the contact hole with reference to FIG. 5. In FIG. 5, the reference metal, 2 designates a silicon substrate as a semiconductor substrate which is for example a P type substrate. The reference numeral 4 designates a diffused layer of an n+ type for example which is formed in a part of the upper surface of the substrate 2, and the reference numeral 8 designates a contact hole which is formed by etching selectively away a part of an insulating layer 6 made of SiO2 or the like. In this connection, a bottom layer 10 within the contact hole 8 is formed of a titanium film which is formed in order to come in ohmic contact with the diffused layer 4. This titanium film may be formed by utilizing the CVD (Chemical Vaper Deposition) or PVD (Physical Vaper Deposition) method. 12 designates a barrier film, made of titanium nitride, which is formed so as to cover the inner surface of the contact hole 8 and its peripheral area. After forming this barrier film, the contact hole 8 is filled with metal such as aluminium alloy. The above-mentioned barrier film serves to prevent the silicon substrate or the multilayer metallization structure from coming directly in contact with the filling metal, thereby suppressing the occurrence of the above-mentioned phenomena such as the suction effect (diffusion effect) and the like.
When the process of forming the titanium film has been completed, the process of forming the barrier film is carried out to form the structure in which the barrier film is directly laminated on the titanium film as described above and, the phenomenon occurs in which the barrier film is peeled off from the titanium film. As for this cause, it can be considered that Ti crystal which is formed in the process of forming the titanium film reacts on the process gas (e.g., titanium tetrachloride (TiCl4) gas) which is used in the process of interest so that Ti crystal is partially etched away and as a result the tightly contacting portion between Ti crystal and the substrate becomes slender to reduce the bonding strength between Ti crystal and the substrate. In addition, the phenomenon occurs in which the constituent components of the process gas (e.g., TiCl4 gas) which is used in the process of forming the titanium film diffuse into the titanium film. Both the phenomenon in which the barrier film is peeled off from the titanium film and the phenomenon in which the constituent components of the process gas diffuse into the titanium film result in the electrical resistance of the lamination body consisting of the titanium film and the barrier film being increased.
In order to prevent these phenomena, after the process of forming the titanium film 10, the process of nitriding the surface layer of the titanium film to form thereon a nitride layer is carried out. By carrying out this process, the nitride layer 13 is formed on the surface of the titanium film. Then, the barrier film 12 formed of the above-mentioned titanium nitride film is formed on the nitride layer 13. Conventionally, the process of nitriding the surface layer of the titanium film to form thereon the nitride layer is carried out in such a way that the substrate 2 is annealed by being heated up to 800xc2x0 C. for example using a lamp at the atmospheric pressure in N2 ambient.
In this conventional process, the substrate is, after forming the titanium film 10, transferred to another reaction chamber for annealing. During this transfer, the substrate is subjected to the atmosphere so that a TiO2 film and the like each having a high resistance value are inconveniently formed on the titanium film 10.
In order to prevent this phenomenon, there has been developed the method wherein the process of forming the titanium film 10 on the substrate and the process of nitriding the surface layer of the titanium film 10 to form thereon the nitride layer are continuously carried out in the same reaction chamber.
More specifically, the titanium film 10 is firstly formed on the substrate in the reaction chamber by utilizing the CVD method employing the process gas of the mixed gas consisting of titanium tetrachloride (TiCl4) gas, H2 gas and Ar gas. Then, the substrate 2 is subjected to plasma processing in an atmosphere of gas used to nitride the titanium (e.g., NH3 gas) in the same reaction chamber in order to form the nitride layer 13 on the surface of the titanium film 10.
In this conventional method, since both the process of forming the titanium film 10 on the surface of the substrate 2 and the process of forming the nitride layer 13 on the surface of the titanium film are carried out in the same reaction chamber, it is prevented that the TiO2 film as described above is formed, but a new problem occurs.
That is, when the titanium film 10 is being formed by utilizing the CVD method, the white or black complex (e.g., TiClx (x=2 to 3)) containing therein Ti by-product is adhered to the internal surface and the like of the reaction chamber. When completing the next process of nitriding the surface layer of the titanium film to form thereon the nitride layer in the same reaction chamber, that by-product comes off the internal surface of the reaction chamber down onto the substrate to contaminate the substrate. This is a problem.
In addition, in the above-mentioned conventional method, there arises the problem that the electrical resistance value of the titanium film is increased due to the phenomenon that the constituent components of the process gas (e.g., TiCl4 gas) diffuse into the titanium film as described above.
The present invention was made in order to solve the foregoing problems associated with the method wherein the titanium film and the barrier film are continuously formed, by lamination, on the surface of the substrate as described above through the continuous processes therefore.
It is therefore an object of the present invention to reduce the by-product which is adhered to the internal surface of the reaction chamber in the process of forming the titanium film on the substrate which come off from the internal surface of the reaction chamber down onto the substrate to contaminate the substrate.
It is another object of the present invention to reduce the electrical resistance value of the titanium film formed on the substrate.
Other objects of the present invention will be apparent from the following description.
According to a first aspect of the present invention, there is provided a method for forming a titanium film and a barrier film on a surface of a substrate by lamination, the method comprising the steps of: forming the titanium film on the surface of the substrate using a first process gas containing therein TiCl4 and a reducing gas; forming plasma above a surface of the titanium film formed on the surface of the substrate using a second process gas containing therein N2 gas and a reducing gas; decreasing Cl in the titanium film by decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma; and forming the barrier film on the nitrided titanium film, the second process gas containing N2 gas in a ratio of 0.5 or lower with respect to the reducing gas.
In the method, the reducing gas contained in the first process gas is preferably one of H2 gas and SiH4 gas.
Further, the reducing gas contained in the second process gas is preferably one of H2 gas and NH3 gas.
It is preferable that the step of forming the titanium film and the step of nitriding the surface of the titanium film be carried out by Chemical Vapor Deposition (CVD).
It is also preferable that the barrier film be a TiN film.
According to a second aspect of the present invention, there is provided a method for forming a titanium film and a barrier metal film on a surface of a substrate by lamination, the method comprising the steps of: forming plasma and the titanium film on the surface of the substrate using a process gas containing therein TiCl4 and a reducing gas; decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, decreasing Cl in the titanium film and the surface thereof, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma, the step being carried out under the conditions of
an H2 gas supply rate of 500 to 3000 sccm,
an N2 gas supply rate of 300 to 1000 sccm,
a nitriding temperature of 550 to 800xc2x0 C.,
a nitriding pressure of 0.5 to 10 Torr, and
an RF power of 500W at 13.56 MHz; and
forming the barrier film on the nitrided titanium film.
In the method, the step of decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, decreasing Cl from the titanium film and the surface thereof, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma is preferably carried out under the conditions of
an H2 gas supply rate of 1500 sccm,
an N2 gas supply rate of 500 sccm,
a nitriding temperature of 580 to 700xc2x0 C.,
a nitriding pressure of 1 to 5 Torr, and
an RF power of 500W at 13.56 MHz.
It is preferable that the step of decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, decreasing Cl in the titanium film and the surface thereof, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma be carried out for 10 to 120 seconds.
Further, it is further preferable that the step of decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, decreasing Cl in the titanium film and the surface thereof, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma be carried out for 30 to 60 seconds.
In the methods according to the first and second aspects, the substrate is preferably an Si wafer.
In the methods according to the first and second aspects, the step of decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, decreasing Cl in the titanium film and the surface thereof, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma is preferably carried out at a pressure higher than that in the step of forming the titanium film.
In the methods according to the first and second aspects, the step of decreasing TiCl4 remaining in the titanium film and on the surface thereof by the reducing gas in the plasma, decreasing Cl in the titanium film and the surface thereof, and simultaneously nitriding the surface of the titanium film by N2 gas in the plasma is preferably carried out at a temperature higher than that in the step of forming the titanium film.
In the methods according to the first and second aspects, the titanium film formed on the surface of the substrate preferably has resistivity of 200 xcexcxcexa9xc2x7cm.
According to a third aspect of the present invention, there is provided a method of forming a titanium film and a barrier film on a surface of a substrate by lamination, the method comprising the steps of:
forming titanium film on the surface of the substrate using process gas containing therein TiCl4;
subjecting the substrate having the titanium film formed thereon to a plasma process using a second process gas containing therein both nitrogen gas and hydrogen gas, thereby nitriding a surface layer of the titanium film to form thereon a nitride layer; and
forming a barrier film on the titanium film having the nitride layer formed thereon.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.